The present invention relates generally to valving devices. More particularly, the invention relates to a pilot valve for regulating hot gases from a rocket motor or gas generator to a reaction jet.
The U.S. Government may have certain rights in this invention.
Pilot valves are frequently used in missile and space vehicle flight control systems to control the reaction jets that vary the pitch, yaw, spin rate and other dynamic characteristics of a vehicle in flight. The pilot valve enables on/off control over the propulsive gases, typically comprising the output of a solid rocket motor or gas generator, supplied to the jet nozzle. The pilot valve accomplishes this by allowing venting and pressurization of a main stage actuation chamber operatively disposed with the jet nozzle. Such pilot valves typically are single stage in configuration and may utilize a solenoid-actuated flapper valve that, when in a first position, permits high temperature pressurized gas to be communicated to the actuation chamber, thereby activating a valve that causes flow through the jet nozzle to be shut off. When in a second position, the flapper valve permits the actuation chamber to communicate residual pressurized gas therein to a vent port, thereby allowing deactivation of the valve and flow through the jet nozzle to be initiated or resumed. Additionally, because the gases flowing through the pilot valve may exceed 3500 degrees Fahrenheit, each valve component that may be exposed to these gases must be capable of withstanding these high temperatures.
Among the disadvantages of single stage valves is sensitivity to leakage of the main stage actuation chamber if the valves are sized sufficiently small to provide a fast response time. Further, if single stage valves are sized to accommodate main stage leakage, they require relatively high solenoid power and achieve unacceptably low response rates. Because missiles and space vehicles typically move at high rates of speed, it is critical to the control of such craft that the reaction jets have a high rate of response between their respective on and off positions.
Two-stage pilot valves are known in the art. For example, U.S. Pat. No. 5,117,868 (xe2x80x9cthe ""868 patentxe2x80x9d) discloses a valve for use in conjunction with aircraft flight control hydraulic systems. The valve has a main stage comprising a pressure inlet chamber having an inlet port, a service chamber having a service port and a return chamber having a return port. A moveable main valving element is urged by a valve spring housed within a spring chamber into a first position for shutting off the service chamber from the pressure inlet chamber and communicating the service chamber to the return chamber. The pressure inlet chamber is connected via an internal duct to the spring chamber such that the valve spring is exposed to working fluid. Components of the valve disclosed in the ""868 patent (e.g., the spring and spot valve) are not likely to function reliably if exposed to high temperature rocket exhaust gases. Accordingly, the valve disclosed in the ""868 patent is not suitable for reaction jet flight control systems.
Accordingly, a need exists for a multi-stage directional pilot valve that can accommodate high temperature gas flow associated with solid propellant propulsion therethrough.
In accordance with the present invention, a multi-stage pilot valve is disclosed for selectively supplying high temperature gas to and venting gas from a reaction jet main stage actuation chamber.
In a preferred embodiment of the invention, the pilot valve comprises a solenoid actuated ball and socket flapper valve having a pressure inlet, an exhaust outlet and a service port. The first stage service port is in fluid communication with a second stage actuation chamber. A piston disposed in the second stage actuation chamber operatively engages a ball member of a ball-and-seat type valve comprising the second stage valve. The second stage valve also comprises a pressure inlet, an exhaust outlet and a service port. The piston and ball are sized relative to each other such that when the second stage actuation chamber is pressurized by the first stage, the force acting on the piston is sufficient to seat the ball against the second stage pressure inlet. This shuts off the flow of high pressure gases to the second stage service port and permits the second stage service port to vent through the exhaust port thus venting the reaction jet main stage actuation chamber.
When the second stage actuation chamber is vented by the first stage valve, the pressure acting on the ball is sufficient to overcome the force acting on the piston. This opens the second stage pressure inlet to permit high pressure gases to enter the ball chamber and exit through the second stage service port. The pressure in the ball chamber seats the ball member against the second stage exhaust outlet seat, shutting off communication between the second stage service port and the exhaust port.
The bi-directional movement of the ball member of the second stage valve is accomplished entirely by fluid pressure, thus enabling a fast responding, high flow rate regulation of the hot gases without the use of springs or other resilient members that would be of dubious reliability operating in a hot gas environment.